Turpentine is the general term for the volatile oil present in trees, primarily coniferous trees. Chemically, it is predominately a mixture of unsaturated mono- and bi-cyclic C.sub.10 H.sub.16 terpenes. The principal component is alpha-pinene, which is present in the turpentine from all species of turpentine bearing trees.
The composition of the turpentine is determined by the species of the tree. A chromatograph of the turpentine makes a good fingerprint for identifying the species.
Although over thirty compounds have been identified in turpentine only a few have commercial significance, that is, they can be separated in high purity for subsequent use. Alpha-pinene, beta-pinene, and beta-phellandrene and dipentene are present in large enough volume in gum or sulfate turpentines of most species to make isolation feasible. .DELTA.-3 carene is present in large quantities in certain species, especially in the northwestern and Scandinavian pines. The terpenes undergo numerous reactions including hydrogenation, isomerization, polymerization, oxidation, halogenation, esterification and dehydrogenation.
There has been and continues to this day investigations concerning the production of high volume chemicals from nonpetroleum base sources. Trees, especially coniferous trees, are a renewable resource that can be ground into wood chips and have extracted therefrom resins and terpenes. Terpenes are therefore a renewable resource that may be used to replace the present petroleum base source of most of industry's hydrocarbons. However, a turpentine or a mixture of terpenes, in and of itself, is not a commercially significant hydrocarbon feed stock. Therefore, a process that will readily convert a terpene or a turpentine feed stock into a valuable or commercially more acceptable compound is highly desirable.
In the past numerous publications have reported the conversion of turpentine to various chemical compounds using numerous reaction conditions and catalysts. More specifically, U.S. Pat. Nos. 3,780,124; 3,780,125; 3,700,746; 3,700,747, and 3,642,928 all disclose the use of zeolites to isomerize terpenes to limonene. In U.S. Pat. Nos. 3,359,342 and 3,360,581, Derfer discloses the need to pretreat .alpha.-pinene streams containing catalyst poisons with a Group VIII metal in the presence of hydrogen or with metallic sodium in order to prevent poisoning of the isomerization catalysts. However, none of the prior art publications disclose or suggest the process for the conversion of terpenes to limonene which comprises contacting at least one terpene selected from the group consisting of mono- and bi-cyclic unsaturated hydrocarbons having the formul C.sub.10 H.sub.16 with an alkali metal sulfide catalyst on a carrier at a temperature of 300.degree. to 450.degree. C. at a LHSV of 0.20 to 20.